Compass indication stabilizing system



March 22, 1949. w. P. LEAR 2,465,311

COMPASS INDICATION STABILIZING SYSTEM Filed Oct. 30, 1945 2 Sheets-Sheetl REMOTE INDlCATORS DIRECTIONAL CONTROL UNIT .BY v

ATTORNEY March 22, 1949. w, LEAR 2,465,311

COMPASS INDICATION STABILIZING SYSTEM Filed Oct. 30, 1945 2 Sheets-Sheet2 A TTORNEY Patented Mar. 22, 1949 William P. Lear, North Hollywood,Calif., assignor, by mesne assignments, to Lear, Incorporated, GrandRapids, Mich, a corporation of Illinois Application October 30, 1945,Serial No. 625,492

1 12 Claims.

This invention relates to stable directional compass systems,particularly for use aboard aircraft and self-orienting remoteindicators actuated thereby. The present application is in part acontinuation of my copending application Serial No. 454,559 filed August12, 19 2, now Patent No. 2,403,091, and assigned to the same assignee asthe present application.

In modern armored military aircraft, it is desir able to locate themagnetic compass remote from the instrument panel and pilot so as toavoid indication errors due to the surrounding metallic structure. Thecompass indications are, rurthermore, upset during maneuvering andaerobatics of the aircraft that cause temporary spinning and turningerrors in the magnetic compass needle indications. The present inventionis directed towards a directional compass system wherein the indicationsare substantially stable during aircrait'maneuvers. Towards this end adirectional gyroscope is electronically related with the magneticcompass in a manner to stabilize the resultant bearing indications.

In accordance with the present invention, I provide a simple, reliableand effective stabilized directional compass system. The magneticcornpass is merely electrically coupled to the system. A standardcompass is employed, whichinaybe placed anywhere on the alrcraftso as tobe relatively unaffected by the metallic structure and armor. Spinningor turning reactions in the magnetic compass are averagedout in thesystem and do not erroneously affect the resultant indications. Thedirectional gyroscope isinherently lazy and stable over short periods oftime, and the composite efiect with the magnetic comp-ass is toaifordstabilized directional indications .th at have an overall accuraterelationship to true north.

An importantifeature of the present invention is thesubstantially-torqueless pick-off of both the magnetic and gyroscopecompass bearings for eiiecting the orientation control on the gyroscope.In prior systems, errors were introduced in the resultant readings ofthe system due to the nature and arrangements of the pick-off devicesemployed. The precessional errors which the directional gyroscope slowlytends to accumulate during flight are continuously and'automatically corrected with themagnetic-compass as a reference through the .intercoupledelectronic control unit of the invention. This system is often referred'to 'as a northerlyseeking directional. "gyroscope.

Both the magnetiocompass and directional gyroscope used are of standardsize and or conven- 'tional gyroscope may tend toaccumulate.

tional design and construction, as are the other components of mysystem.

Large modern military aircraft generally re.-- quire a number of remotecompass indications throughout the aircraft, so that the copilot,navigator, bombardier, and others thereon may have continuous, directand stable bearing indications. The compass directional systems of theprior art provided only a limited number of remote indicators. Animportant aspectiof the system of my present invention is the provisionof any number of remote compass indicators. These indicators areactuated by locally generated electronic control currents. They areselfsaligning, and correspond with the direction of the stabilizeddirectionm readings. The remote compass indications are substantiallyunaffected by gyractions to which the magnetic compass may betemporarily subjected, or precessional errors which the direc- Thuscontinuous accurate compass bearingsare simultaneously providedthroughout the aircraft, without loading or otherwise reflecting errorsback onto the compass units.

A further importantieature of the present ,invention is the use ofpolyphase telemetering pick-off units for each of the gyroscope, magnetic compass and remote indicators.

Still another feature of the invention is the provision of a balancedelectrical bridge circuit interconnecting-the pick-ofif.units forthe-gyroscope and .the magnetic compass to control the correctiveprecessional movement on the yroscope in accordance with the magneticcompass indications.

These and other advantages, objects and capabilities of my presentinvention will become more apparent in the following description ,of apre ferred embodiment thereof, shown in the accompanying drawings, inwhich:

Fig. 1 is a diagrammatic representation of the invention system.

Fig. 2 is a schematic electrical diagramof one embodiment which myinvention may assume in practice.

Fig. 3 is a diagrammatic xcpresentation of another embodimentoi myinvention.

Fig. 4 isa schematic electrical diagram of modified form of the systemcorresponding to Fig. 3.

Referring to thedrawingait willoe noted that the essential components ofthe inventionsystem are a directional gyroscopeglll, a;m agnetic compassit, an intercoupled electronic directional control unit 28?, and remoteindicators "-25 and 26. The system is energized by a local polyp-hasealternating current source it that is generally present aboard anaircraft. A three phase supply is indicated, although other polyphasesystems may be used. In a manner to be described more particularlyhereinafter, the directional gyroscope, magnetic compass and remoteindicators are each provided with pick-off units, and the statorwindings of the pick-off units are energized from the source H, to whichthe stator windings of the pick-off units are symmetrically connectedelectrically. The pick-off unit associated with the directionalgyroscope thus corresponds to a transmitter element of a poiypnaseself-synchronous type 01 telemetering arrangement. The pick-orf unitsassoc1ated with the magnetic compass and the remote indicators 25 and rtcorrespond to receiver elements of such self-synchronous type ortelemetering arrange ment.

Briefly speaking, in the event the rotors of the gyroscope it] and themagnetic compass are out of their predetermined directional alignment,the pick-off units Will be eil'ective to actuate the directional controlunit ill which will effect a precessional corrective movement on thegyroscope rotor to restore the gyroscope compass to its predetermineddirectional alignment. The remote indicators are coupled to thegyroscope to repeat its readings through the association of threspective pick-n units. The connections of the gyroscope and thecompass to their pickoff units are substantially torqueless, so thatsubstantially no torque is exerted on the rotors of the gyroscope ormagnetic compass. This assures accurate directional alignment of thegyroscope compass and remote indicators as the corrective action isaccomplished with negligible drag or torque which might interfere withaccurate directional alignment. As will be apparent as the descriptionproceeds, any number of remote bearing indicators may be incorporatedwithout introducing drag on either the gyroscope I 0 or the compass l5.

The directional gyroscope Ill is of the conventional type, comprising arotor l2 mounted with three degrees of freedom, and which may beelectrically or pneumatically driven as will be understood by thoseskilled in the art. The gyro rotor I2 is spun about a horizontalspinning axis supported in a gimbal ring 13, which in turn is freelymounted on bearings M in vertical ring I6. The vertical ring it isrotatably supported about a vertical axis on bearings ll of thegyroscope, and a circular directional scale i8 is supported on thevertical ring l6, and Viewed through a window I9 in the gyroscope casingii.

The gyro indications correspond to the reading of scale l'8 opposite theusual index or lubber line marked on window l9. The conventionalauxiliary mean-s for driving and caging the gyroscope, not shown, are tobe understood as incorporated in the schematically representeddirectional gyroscope H3. The gyroscope I 0 is of standard size anddesign, being additionally provided with a precession correction winding22 mounted Within the casing 2|, and concentric about horizontal gimbalring I3. The winding 22 is connected to the directional control unit 28by leads 24, 21 and 28. The control signal introduced into thedirectional control unit 20 from the pick-01f units, in a manner to bedescribed hereinafter, generates a control current at the output of theunit 20 which is selectively applied to the winding 22 through the leads24, 21 and 28. The unidirectional corrective flux selectively producedin the winding 22 reacts with permanent magnets 29, 29 secured to thehorizontal gimbal ring The corrective force thus exerted on the magnetsis in a direction so as to counteract any precessional or turning errorsthat the gyroscope might tend to incur. In this manner, and as will bemore apparent hereinafter, the orientation and indication o1 thegyroscope are made stable, and tied to the true magnetic northindications of the magnetic compass l5.

A bearing pick-off unit ill! is supported on a plate 3| that is mountedon top of easing 2!. Unit comprises a central vertical shaft 32 which isecured to vertical ring l6 of the gyroscope. Practically no torque orforce is imparted to the gyroscope by unit 30, as will hereinal'ter beset forth in more detail. The directional position of the gyroscope isin this manner directly communicated to unit 20.

Unit corresponds to one component of a polyphase self-synchronous typeof telemetering arrangement, and includes a polyphase stator windingenergized by the local alternating current source H through leads 33.The rotor of unit 30 is connected by leads 34 to directional controlunit 26. In a manner to be described, a control signal from unit 35 iscombined in unit with a control signal from a corresponding pick ofl?unit on magnetic compass I5 to produce a unidirectional control currentthrough coil 22. A unidirectional corrective flux is produced by coil 22that reacts with the permanent magnets 29 secured to horizontal gimbalring I3. The

- corrective force thus exerted on magnets 29 is in a direction so as tocounteract any precessional or turning errors that the gyroscope maytend to incur. In this manner, the orientation and indications of thegyroscope are made stable, and tied to the true magnetic northindications of magnetic compass l5.

The magnetic compass I5 is of standard size and of the conventionaldesign generally used aboard an aircraft. It is a master magneticcompass, containing a substantial magnetic bar which is mounted for freemovement in azimuth for alignment with the earths magnetic field. Barmagnet 5| is within a float 52 which is pivotally supported within afluid 53 in the housing of the compass I5. A pivot spindle 54 is securedto float 52 and supports the float and magnet bar 5| on a jewel bearing55. A spring 56 supports bearing 55 and also float 52 in a resilientmanner. Magnet bar 5| is thus freely supported for alignment with theearths magnetic field, fluid 53 serving to damp the movement of themagnet as well as relieve the pivot pressure on bearing 55.

A directional pick-off unit 60 identical in construction with the unit30, is mounted on the casing of compass l5 and the directionalorientations of magnet bar 5| are communicated to the pick-off unit 60,as follows. A small magnet bar 6| is mounted at the upper end of spindle54 and a second magnet 62 is mounted above magnet Gl and serves as afollow-up or slave magnet. Magnet 62 is connected to the rotor ofpick-off unit 60 through shaft 63. The azimuthal bearing indications ofthe main compass bar 5| are thus faithfully communicated to the rotor ofpick-off unit 59. Such action is with the application of negligible dragor torque which might interfere with accurate directional alignment ofmagnet bar 5|. The stator windings of the unit 60 are connected toalternating current source 5 I I symmetrically with the stator windingsof unit 30, through leads 35. The rotor of unit 60 is connected by leads36 to directional control unit 20.

When gyroscope l and magnetic compass I are in directional alignment,the rotors of units 30 and E0 have a predetermined angular relationwithin their respective stator windings. Generally, this angularrelation is 90. Under these conditions, no output is produced from unitZll to energize coil 22.

However, in the event rotor it of gyroscope H3 is rotated out ofalignment with the magnetic bar 5| of compass iii, the resultantrelative displacement from their predetermined angular relation, ornull, of the rotors of units Ell, produce control signals indirectional. control unit 20. Such control signals effect theaforementioned iiow of a unidirectional current through coil 22 toprovide: a unidirectional magnetic flux acting on magnets 29. r gnitudeof the voltage produ ed across the ter of coil 22 is substantiallyproportional to anion v-.t of relative displacement from null of therotors of units til and 65), and the direction of the produced in coil2:2 is such as to rotam rotor of gyroscope it back into itspredetermined alignment magnet bar 5i of cornoass De sirably, thesignals from units ilil and amplified in unit before being com I obtainan increased sensitivity of the control action on gyroscope lll.

Remote indicators 25 and 26 each co: pick-oil unit of the same type uniso, with the rotors thereof tied to rotate dicating needles 3i and 33 ofindicators 25. Leads 46 and t2 connect the rotors of indicators 25, lidrespectively, to a bus l-f'i intercom nected by leads M to directionalcontrol unit Other leads interconnect the stator ings of the remoteindicators to local alternating current source ii, and symmetricallywith the stator windings of units 598 and 68. Due to such symmetricalconnection, t e rotors of the remote indicator tend to retain apredetermined direc tional alignment with the rotors of units 38 and andwill. thus follow changes the directional bearings of gyroscope l3 andin lo compass l5. Preferably, the remote indicators are tied solely tothe gyroscope, which is in turn under the control of magnetic Thus, inpractice, the orientation or hearing positions of gyroscope it are tiedto or otherwise made to correspond with the azimutl' al hear ingpositions of compass it. Both re; ngs made to refer to true north as theierence, with the magnetic compass finding such north and the gyroscopebeing made to assume and maintain such spatial reference. The magneticcompass bar ill naturally assumes such north position, or otherwiseaverages out its gyrations to efiective north position.

The operation of the system in detail will be understood more clearly byreference to Fig. 2 which is a schematic wiring diagram of oneembodiment of the system, including gyroscope it, magnetic compass iii,remote indicators 25, 2t, and associated pick-oif units. The pick-cf":unit 3t associated with gyroscope ill includes a rotor winding litconnected to shaft 32 and a three phase stator winding 55, t'l, E58connected by leads 3% to local alternating current source ll. Similarly,pick-off unit Ell associated with magnetic compass it, includes a rotorwinding coupled to sha'.t E3 and three phase stator Wind- 6 loge ll, :2,13 connected by leads 35 to source it symmetrically with the three phasestator windings of unit 36.

The remote indicators 25, 25 comprise pickoil un l5, '55 similar tounits 30 and 6t! and each icludes a rotor winding M, M coupled to 3? or38. The pick-off units further include three phase stator windings l6,i3 and m 'll, connected respectively by conductors t? and ll to sourcell symmetrically with the stator windings of units 30 and Gil.

Due to the symmetrical connection of the stator windings oi the severalpick-off units to source 5 i, the polyphase fields of the statorwindings il be in the same space and time phase relation, is well-knownin the art. Rotation of each of the rotors within its respective statorwill result in the development of an output potential across theterminals of the rotor. However, when the rotor wirdings are in theirpreed angular or null relati with each other within their respectivefield wr. o potentials oppose each other and nullify any control.action.

In practice, the orientation or bearing posioi gyroscope 5d are tied toor otherwise mad to correpond with the azimuthal bearing p0 of magneticcompass E5. Both readare thus made to refer to true north as a once. Themagnetic compass l5 finds such north and the gyroscope H3 is made toassume an" thin such spatial reference. The magcompass i5 is moresensitive to aerobatic noes due to the aircraft, but its northerly oneaverage out over a period of time. In flight, its indications are quitestable.

--ily turning or precessional errors are on in'lulative only over asubstantial period of amounting to at least several minutes. Theprecessional control action of compass ill on osccpc it through con rolunit ill and coil ode to he only slowly effective, so as not .0 thenormally stable indications of upsets of magnetic compass bar 55. It isthus unnecessary to adjust the gyroscope it periodically forprecessional errors, since such errors automatically eliminated byreference to and control by the average northerly readings of magneticcompass it.

One terminal of rotor winding is grounded ill and the other terminalthereof is connected through. a lead 3 to the control grid 82 of anelectronic amplifier tube 89. Cathode 83 of tube 8% is connected toground through a phasing resis'or and condenser combination a l, 85 anda resistance 8% provides the bias for grid 82. The 18+ bias for anode 8?of tube 80 is provided through a resistor Anode 8? is capacitancecoupled to control grid i l of a second electronic amplifier tube 9i!through a coupling cor riser $2. Cathode 93 and control grid Ell areconnected in the same fashion as no corresponding elements of tube The13+ potential for anode lid is provided through a primary Winding lid ofa transformer Q5, and s e gr; 2? is connected to one terminal of windingThe amplified potential from rotor winding is thus applied to primarywinding t6.

Secondary winding or of transformer 95 is connected in electric circuitrelation with one coil 88 of a dynamometer relay Hid having a movablecontact lfll. The pivot point of contact Ml 7 is connected to oneterminal of a suitable battery I02 which has its opposite terminalconnected to the mid-point of coil 22 by conductor 2i. The terminals ofcoil 22 are connected by conductors and 28 to contact points tilt, HMassociated with contact Ilil. Thus, by engagement of contact Hit Witheither of its associated contact points, a uni directional current isprovided through one-half or the other of coil 22 to provide aunidirectional flux for magnets 29 in a direction to induce a correctiveprecessional action on rotor ii of gyroscope Ill.

On terminal of rotor winding ill of pick-off unit 60 is grounded and thepotential from the other terminal thereof is applied through con--ductor 36 and capacitance coupled electronic amplifier tubes I05, Hi! toa primary winding Hi5 of a transformer IN. The circuit connection of theelements of tubes I95 and lid are the same as those of tubes 3t and st,respectively, and specific description thereof is believed unnecessary.The secondary winding its of transformer W2 is connected in series withthe other operating coil III of relay Idfi. A conductor H2 connects thecommon junction l I3 of coils 98 and ll! to the common junction Il iofsecondary windings 9'2 and I08.

The arrangement thus far described operates in the following manner.When rotor windings 65 and I are in their predetermined null relationship, which occurs when gyroscope it; and magnetic compass 55 are intheir predetermined directional alignment, the amplified potentials fromrotor windings E and ii! are such as to oppose each other, and thusproduce no action of relay I00. Should gyroscope move out of suchdirectional alignment with magnetic cornpass I5, there will be anangular difference from null betwen the relative positions of rotorwindings 65 and Ill within the respective stator windings. The amplifiedpotentials from the rotor windings will therefore no longer be equal inmagnitude and opposite in direction.

Accordingly, operation of relay ills will be effected to swing contactill! to engage either contact IE3 or Illll depending upon the d notionof the movement of gyroscope it out of directional alignment withmagnetic compass The cuit connections are so chosen that theTESlli'ifll.

unidirectional current flow through coil is in a direction to produce aunidirectional magnetic flux effecting movement of magnets 29 in adirection to bring gyroscope til back into the predetermined directionalalignment with magnetic com" pass I5. At the same time, rotor windin E5is moved back into its predetermined angular or null relation with rotorwinding 3. The amplified potentials from the rotor windings thereuponare substantially equal in magnitude and opposite in direction so thatrelay Eilii becomes deenergized.

The rotors M, M of receiver units is, 55 connected to remote indicators25, are tied into predetermined angular relation with the rotor winding65 of gyroscope pick-off unit in the following manner. A third winding52$ is provided on transformer 95 and its "CWO outer terminals areconnected to the control grids i it, I ll of a pair of amplifier tubesNil, 225. cathodes I I8, I2I of the tubes are interconnected to groundand to the center tap of winding lib through a biasing resistor IE2.Anodes l23, l2 i are each connected to an outer terminal of a primaryWinding I26 of a transformer 33. The center tap of winding I26 isconnected to B+. Secondary it winding I21 of transformer I3!) isconnected to bus 43, one conductor of which is grounded at I28.

The amplified potential from rotor winding 65 is thus applied to bus 43to which the potentials from rotor windings 1 3, H, are likewiseapplied. If there is a difference between the two potentials applied tobus at, as will occur when rotor winding 65 is out of its predetermineddirectional alignment with rotor windings id, i l, a torque is impressedon rotor windings M, 'M in such a direction as to rotate these rotorwindings back into their predetermined angular relation with rotorwinding 65. At such predetermined angular relation, remote indicators25, 26 correspond in directional alignment with gyroscope ill. Thedirectional indicators are thus effectively tied to gyroscope I0 which,in turn, is tied to magnetic compass I5.

Fig. 3 is a diagrammatic representation of a directional control systemin which the dynamometer relay Illtl of Fig. 2 is replaced by apolarized electrical bridge circuit Elements of Fig. 3 corresponding tothe same elements in Fig. 2 have been given the same referencecharacters. The amplifiers associated with each of coils 65 and 10 havebeen schematically illustrated in block form at Ifiii and I222. Theouter terminals of winding cl of transformer are connected throughpolarizing rectifier-s I34 to junction points I36, Nil of electricalbridge circuit I35. Conductors 2d, 23 connect precession coil 22 ofgyroscope lil across these junction points. A conductor I38 connects themid-point of winding 9? to one terminal of winding Hill of transformerIlll. The other terminal of winding I08 is connected in parallel throughvoltage limiting resistors I lI, M2 to junction points I3ti, I37. Thevalues of resistors It i, i 22 are so chosen that the effectivepotential of the full winding IE8 at junction points n33, till is equalto the potential of one-half of winding til at each of these points.

The described arrangement of 3 operates in the following manner. Whenrotor windings 65 and Ill are in their predetermined null relation, theoutput potentials thereof are equal and opposite. Accordingly, thepotentials at points I36 and I3? are equal, and there is no potentialdifference across coil 22. Should there be a displacement from null ofwinding 65 with respect to winding it, there will be a displacement inphase of the alternating current potential from rotor Winding 65 withrespect to that from rotor winding it. Thus, at any particular instant,the potential at the terminals of winding 91 will not be equal in valueto the potential applied to junction points Sit, lii'l from winding I08.As there is a difference in potential between junction points I38 andI3? a unidirectional current will flow through coil effecting acorrective precessional action on the rotor of gyroscope It] in themanner previously described. The maximum difference in potential atjunction points I36 and I3? occurs when windings 65 and I0 have anangular relation of either 0 or The potential developed by the two rotorwindings are equal and opposite at points 535, I31 when the windings are90 apart with respect to their developed output potentials.

Fig. 4 is a schematic electrical diagram representing a modification ofthe circuit shown diagrammatically in Fig. 3, and corresponding elementshave been given the same reference characters. The output potential ofrotor winding 10 is applied through leads 36 to the primary winding I44of a transformer I45. The terminals of secondary winding MB oftransformer I45 are connected to control grids I41, Hi8 of a dualamplifier tube I58, whose anodes lI, I52 are connected to the oppositeterminals of a primary winding I53 of a transformer I55. The center tapof winding I53 has a direct current positive potential applied theretofrom a battery E54. The center terminal of winding I 15 is grounded andconnected through a potentiometer Ebb and a resistor I51 to the dualcathode I58 of tube Hit. The negative terminal of battery 55% islikewise grounded. Resistor I57 provides a grid bias for tube I50, andthe purpose of potentiometer will be described :iore fully hereinafter.

The output of rotor winding 65 is impressed through lead 34 upon theprimary winding ltl of a transformer I68 having the terminals of itssecondary winding 562 connected to the control grids i63, 564 of a duaicathode amplifier tube I65. The center terminal of winding it? isconnected to ground and through a grid bias resistor I66 to the dualcathode it? of tube W5. Anodes I? I, I12 of tube I55 are connected tothe opposite terminals of a primary winding H3 of a transformer I15, andthe center tap of winding lid is connected to the positive terminal ofbattery iii l to apply the 13+ voltage to anodes ill, H2. TransformersI55 and I15 correspond, in effect, to transformers Iii! and 55 of thearrangements shown in Figs. 2 and 3.

One of the terminals of secondary 5 id of transformer IE5 is connectedto the dual cathode ill of a dual rectifier tube its corresponding tothe polarizing rectifiers I33, I34 of Fig. 3. The other terminal ofwinding I16 is connected to junctions I35, I31 of bridge I35 throughresistors MI, M2. The common junction of the resistors is groundedthrough condenser I18.

The secondary winding of transformer 515, which corresponds to secondarywinding 9'! of transformer 95, is divided into two sections it! and I82.The inner terminals of these two sections are connected to anodes I83,I86 of tube Idii. The outer terminals of winding sections iBl, I32 areconnected to junction points I36, I31 of electric bridge circuit I35,which junction points are connected through resistors MI. M2 to oneinner terminal of secondary winding 1'15 in the same manner asdiagrammatically illustrated in Fig. 3. Junction points I36, I3? areconnected to ground through condensers I85, it'i and through resistorsI88, I9I to the control grids 92, 693 of a pair of amplifier tubes Hill,I85. A suitable phasing network including resistors I88, 59!, resistorsI94, I95 and condensers 91, @538 and Add is provided, with thecondensers being commonly connected to ground and condenser 26% beingcommonly connected to screen grids 2M and 2&2 of tubes IBEI and H35,respectively. A conductor 203 connects the screen grids to theadjustable contact 204 of potentiometer I56, whereby the screen gridbias may be effectively adjusted.

Cathodes 2B5, 288 are interconnected through condenser 201 to groundand, through a conductor 208, are tied to dual cathode I58 of tube I50.Anodes 2m and ZII are connected through conductors 24, 28 to the outerterminals of winding 22. The center terminal of winding 22 is connectedby conductor 21 to one terminal of the sec-- ondary winding 2I2 of atransformer M5, and the other terminal of winding 252 is connected tothe adjustable contact of a potentiometer 2 52' for providing grid biasfor tubes i943, I85. Primary winding 2I3 of transformer 2I5 is connectedacross one phase of local alternating current source ii, and condensers2 M, 2% are connected across the two halves of winding 22 to by-passalternatin' current therefrom so that substantally only the directcurrent component of the output of tubes i959, I passes through coil 22.Conductors ii connect the rotor winding I4 of unit it associated withremote indicator 25 to a third secondary winding 228 of transformer H5.

The described arrangement operates in a maner similar to that of Fig. 3.The resistors MI, reduce the potential, applied from winding to junctionpoints E38, l3? of bridge circuit to substantially balance the potentialaplied from winding sections it i, E82 to such junction points. Whenrotor windings i5 and ID are in null relation, the potentials at each ofthe junction points are equal in tciagnitude and opposite in polarity.Thus, under such conditions, no potential applied to the control gridsof tubes lilii, E95.

Upon a displacement from null of rotor winding #55, iii, a differencein. potential will be developed between junction points we, i3? applyinga corresponding potential to the control grids of tubes ctivating onetube H39, 595 or the other. Thereby, a unidirectional current is causedto flow through precession coil 22 to effect corrective precessiona].action on gyroscope It in the same manner as previously described. Therate of precession may be adjusted by suitable adjustment ofpotentiometer 2 i2 which determines the grid bias of tubes E98, E95, andthus the relative potential at which these tubes become conductive toeffect a current flow through coil 22. Such precession rate may also beadjusted by suitable adjustment of contact 23 1 along potentiometer 0%to adjust the screen grid bias of tubes W0, M5. The rotor winding i l ofpick-off unit 15 associated with remote indicator unit 25, is tied torotor winding 55 in the same manner as previously described.

The described systems of the present invention provide an effectivearrangement for tying the indications of gyroscope id to those ofmagnetic compass l5, so that gyroscope Iii becomes a northerly seekinggyroscope. Also, any number of remote indicators '25 may be effectivelytied to gyroscope iii to provide indications at numerous pointsthroughout the plane. Such arrangement is possible due to theindependent energization of the pick'on units of the remote indicatorsfrom local source ii. The invention system not only provides a sensitiveoperating arrangement but also, due to the amplifiers and thedynamometer relay or bridge circuit arrangements, provides effectiveoperating voltages for application to precession coil 22 to obtainaccurate control of the corrective precessional action on gyroscope iii.

While specific embodiments of the invention have been selected for thepurpose of illustration, it will. be understood by those skilled in theart that the invention may be otherwise embodied without departing fromthe principles thereof.

What is claimed is:

1. A compass system comprising, in combination, a directional gyroscope;a compass; a first rotor winding coupled to said gyroscope and orientedthereby in correspondence with the directional position thereof; asecond rotor windcoupled to said compass and oriented thereby incorrespondence with the directional position thereof; a first polyphasestator winding in inductive relation with said first rotor winding; a-

second polyphase stator winding in inductive relation with said secondrotor winding; said. stator windings being symmetrically connected to asource of polyphase alternatin current and said rotor windings being inelectrically null relation when said gyroscope and compass are in apredetermined directional alignment; and means in circuit connectionwith said rotor windings and operable upon a relative displacementthereof from such null relation, when said gyroscope and compass are outof such predetermined directional alignment, to induce a correctiveprecessional action on said gyroscope to restore such alignment.

2. A compass system comprising, in combination, a directional gyroscope;a magnetic compass; a first rotor winding coupled to said gyroscope andoriented thereby in correspondence with the directional positionthereof; a second rotor windin coupled to said compass oriented therebyin correspondence with the directional position thereof; a firstpolyphase stator winding in inductive relation with said first rotorwinding; a second polyphase stator winding in inductive relation withsaid second rotor winding; said stator windings being symmetricallyconnected to a source of polyphase alternating current and said rotorwindings bein in electrically null relation when said gyroscope and saidcompass are in a predetermined directional alignment; means for alteringthe directional orientation of said gyroscope, including a magnet barsecured to the horizontal gimbal ring of the gyroscope and a coiladjacent said ring; and means in circuit connection with said rotorwindings and operable upon a relative displacement thereof from suchnull relation, when said gyroscope and compass are out of suchpredetermined directional alignment, to induce a corrective precessionalaction on said gyroscope to restore such alignment, including meansconnected to said coil for creating a unidirectional flux about saidmagnet bar.

3. A compass system comprising, in combina tion, a directionalgyroscope; a magnetic compass; a first rotor winding coupled to saidgyroscope and oriented thereby in correspondence with the directionalposition thereof; a second rotor winding coupled to said compassoriented thereby in correspondence with the directional positionthereof; a first polyphase stator winding in inductive relation withsaid first rotor winding; a second polyphase stator winding in inductiverelation with said second rotor winding; said stator windings beingsymmetrically connected to a source of polyphase alternating current andsaid rotor windings being in electrically null relation when saidyroscope and said compass are in a predetermined directional alignment;and means including a dynamometer relay having its energizing windingsin circuit connection with said rotor windings and operable upon arelative displacement thereof from such null relation, When saidgyroscope and compass are out of such predetermined directionalalignment, to induce a corrective precessional action on said gyroscopeto restore such alignment.

4. A compass system comprising, in combination, a directional gyroscope;a magnetic compass; a first rotor windin coupled to said gyroscope andoriented thereby in correspondence with the directional positionthereof; a second rotor winding coupled to said compass oriented therebyin correspondence with the directional position thereof; a firstpolyphase stator Winding in inductive relation with said first rotorwinding; a second polyphase stator winding in inductive relation withsaid second rotor winding; said stator windings being symmetricallyconnected to a source of polyphase alternating current and said rotorwindings being in electrically null relation when said gyroscope andsaid compass are in a predetermined directional alignment; means foraltering the directional orientation of said gyroscope, includin amagnet bar secured to the horizontal gimbal ring of the gyroscope and acoil adjacent said ring; a dynamometer relay operable to connect saidcoil to a source of direct current to create a unidirectional. fluxselectively in either direction about said magnet bar; and means incircuit connection with said rotor windings and. operable upon arelative displacement thereof from such null relation, when saidgyroscope and compass are out of such predetermined directionalalignment, to selectively operate said dynamometer relay to induce acorrective precessional action on said gyroscope to restore suchalignment.

5. A compass system comprising, in combination, a directional gyroscope;a magnetic compass; a first rotor winding coupled to said gyroscope andoriented thereby in correspondence with the directional positionthereof; a second rotor winding coupled to said compass oriented therebyin correspondence with the directional position thereof; a firstpolyphase stator winding in inductive relation with said first rotorwinding; a second polyphase stator winding in inductive relation withsaid second rotor winding; said stator windings being symmetricallyconnected to a source of polyphase alternating current and said rotorwindings being in electrically null relation when said gyroscope andsaid compass are in a predetermined directional alignment; means foraltering the directional orientation of said gyroscope, including amagnet bar secured to the horizontal gimbal ring of the gyroscope and acoil adjacent said ring; a dynamometer relay operable to connect saidcoil to a source of direct current to create a unidirectional fluxselectively in either direction about said magnet bar, and including apair of operating coils; and means, including a pair of electronicamplifiers each connecting one relay coil to one of said rotor windings.and operable upon a relative displacement of said rotor windings fromsuch null relation, when said gyroscope and compass are out of suchpredetermined directional alignment, to selectively operate saiddynamometer relay to induce a corrective precessional action on saidgyroscope to restore such alignment.

6. A compass system comprising, in combination, a directional gyroscope;a magnetic compass; a first rotor winding coupled to said gyroscope andoriented thereby in correspondence with the directional positionthereof; a second rotor winding coupled to said compass oriented therebyin correspondence with the directional position thereof; a firstpolyphase stator Winding in inductive relation with said first rotorwinding; a second polyphase stator winding in inductive relaton withsaid second rotor winding; said stator windings being symmetricallyconnected to a source of polyphase alternating current and said rotorwindings being in electrically null rela... tion when said gyroscope andsaid compass are in a predetermined directional alignment; means foraltering the directional orientation of said gyroscope, including amagnet bar secured to the horizontal gimbal ring of the gyroscope and acoil adjacent said ring; a dynamometer relay operable to connect saidcoil to a source of direct current to create a unidirectional fluxselectively in either direction about said magnet bar; means in circuitconnection with said rotor windings and operable upon a relativedisplacement thereof from such null relation, when said gyroscope andcompass are out of such predetermined directional alignment, toselectively operate said dynamometer relay to induce a correctiveprecessional action on said gyroscope to restore such alignment; aplurality of remote indicators each including a rotatable index; thirdrotor windings each mechanically coupled to one of said indices; thirdpolyphase stator windings each in inductive relation with one of saidthird rotor windings and each connected to the alternating currentsource symmetrically with said first and second stator windings; saidthird rotor windings being in electrically null relation with said firstrotor winding when said indices are in correspondence with theorientation or": said gyroscope and being oriented. to such nullrelation by said third stator windings; and means inductively couplingsaid first and third rotor windings to effect such correspondonce.

7. A compass system comprising, in combination, a directional gyroscope;a magnetic compass; a first rotor winding coupled to said gyroscope andoriented thereby in correspondence with th directional position thereof;second rotor winding coupled to said compass oriented thereby incorrespondence with the directional position thereof; a first polyphasestator winding in inductive relation with first rotor winding; a secondpolyphase stator winding in inductive relation with said second rotorwinding; said stator windings being symmetrically connected to a sourceoi polyphase alternating current and said rotor windings being inelectrically null relation when said gyroscope and said compass are in apredetermined directional alignment; means for altering the directionalorientation of said gyroscope, including a magnet bar secured to thehorizontal gimbai ring of the gyroscope and a coil adjacent said ring; adynamometer relay operable to connect said coil to a source of directcurrent to create a unidirectional flux selectively in either directionabout said magnet bar, and including a pair of operating coils; means,including a pair of electronic amplifiers each connecting one relay coilto one of said rotor windings, and operable upon a relative displacementof said rotor windings from such null relation, when said gyroscope andcompass are out of such predetermined. directional alignment, toselectively operate said dynamometer relay to induce a correctiveprecessional action on said gyroscope to restore such alignment; aplurality of remote indicators each including a rotatable index; thirdrotor win-dings each mechanically coupled to one of said. indices; thirdpolyphase stator windings each in inductive relation with one of saidthird rotor windings and each connected to the alternating currentsource symmetrically with said list and second stator windings; saidthird rotor windings being in elec trically null relation with saidfirst rotor winding when said indices ar in correspondence with theorientation of said gyroscope and being oriented to such null relationby said third stator windings; and means, including an electronicamplifier, inductively coupling said third rotor windings to said firstrotor winding to eiiect such correspondence.

8. A compass system comprising, in combination, a directional gyroscope;a magnetic compass; a first rotor winding coupled to said gyroscope andoriented thereby in correspondence with the directional positionthereof; a second rotor winding coupled to said compass oriented therebyin correspondence with the directional position thereof; a firstpolyphase stator winding in inductive relation with said first rotorwinding; a second polyphase stator winding in inductive relation withsaid second rotor winding; said stator windings being symmetricallyconnected to a source of polyphase alternating current; circuit meansinterconnecting said rotor windings to form an electrical bridge, saidbridge being balanced when said gyroscope and said compass are in apredetermined directional alignment; and means responsive to signalsfrom said bridge, when sa'. gyroscope and compass are out of suchpredetermined directional alignment, to induce a corrective precessionalaction on said gyroto restore such alignment.

9. A compass system comprising, in combina tion, a directional groscope; magnetic compass; a first rotor w ding coupled to saidgyroscope and oriented thereby in correspondence with the directionalposition thereof; a second rotor winding coupled to said compassoriented thereby correspondence with the directional position thereof; afirst polyphase stator winding in inductive relation with said firstrotor winding; a second poly chase stator winding in inductive relationwith second rotor winding; said stator windings being symmetricallyconnected to a source of polyphase alternating cur rent; a balancedbridge circuit, two adjacent arms of the bridge each containing acomponent across which a signal potential derived from said first rotorwindin may be impressed, one or the other of said components beingenergized depending upon the pl of said impressed po tential relative tothat ol the signal derived from the second rotor winding, each said armincluding rectifying t e other two arms of the bridge circuit includingimpedance elements for balancing the bridge to null when said gyroscopeand said compass are in a predetermined directional alignment, thejunction of the arms including said input signal components and thejunction of the arms including said impedance elements defining onediagonal of the bridge being connected to said second rotor winding andmeans connected across the other diagonal of said bridge and responsiveto signals therefrom, when said gyroscope and compass are out of suchpredetermined directional alignment, to induce corrective precessionalaction on said gyroscope to restore such alignment.

10. A compass system comprising, in combination, a directionalgyroscope; a magnetic compass; a first rotor winding coupled to saidgyroscope and oriented ther by in correspondence with the directionalposi ion thereof; a second rotor winding coupled to said compassoriented thereby in correspondence with the directional positionthereof; a first polyphase stator winding in inductive relation withsaid first rotor winding; a second polyphase stator winding in inductiverelation with said second rotor winding; said stator windings beinksymmetrically connected to a source of polyphase alternating current; atransformer including a primary winding and a split secondary winding,circuit means connecting said first rotor winding with said primarywinding, a balanced bridge circuit, two

adjacent arms of the bridge each containing one half of said secondarywinding whereby signal potential derived from said first rotor winding,upon displacement thereof from null, is impressed upon said arms inopposed phase relationship, each said arm including rectifying means,the other two arms of the bridge circuit including impedance elementsfor balancing the bridge to null when said gyroscope and said compassare in a predetermined directional alignment, the junction of the armsincludin said secondary winding and the junction of the arms includingsaid impedance elements definin one diagonal of the bridge beingconnected to said second rotor winding; and means connected across theother diagonal of said bridge and responsive to signals therefrom, whensaid gyroscope and compass are out of such predetermined. directionalalignment, to induce a corrective precessional action on said gyroscopeto restore such alignment.

11. A compass system comprising, in combination, a directionalgyroscope; a magnetic compass; a first rotor Winding coupled to saidgyroscope and oriented thereby in correspondence with the directionalposition thereof; a second rotor Winding coupled to said compassoriented thereby in correspondence with the directional positionthereof; a first polyphase stator winding in inductive relation withsaid first rotor winding; a second polyphase stator winding in inductiverelation with said second rotor winding; said stator windings beingsymmetrically connected to a source of polyphase alternating current; afirst transformer; a second transformer includin a split secondarywinding; a balanced bridge having a first pair of adjacent arms eachincluding impedance means and a second pair of adjacent arms eachincludin one half of said secondary winding and a rectifier in series,the mid-point of said split secondary winding being at one end of theinput diagonal of said bridge and connected to one terminal of thesecondary of said first transformer, the other end of said inputdiagonal being connected to the other terminal of the secondary of saidfirst transformer, the other diagonal of said bridge constituting theoutput terminals thereof; first electronic amplifier means connectingsaid first rotor winding to the primary winding of said firsttransformer; second electronic amplifier means connecting said secondrotor winding to the primary winding of said second transformer; saidbridge bein balanced when said gyroscope and said compass are in apredetermined directional alignment; and means connected across saidoutput terminals and responsive to signals therefrom, when saidgyroscope and compass are out of such predetermined directionalalignment, to induce a corrective precessional action on said gyroscopeto restore such alignment.

12. A system as in claim 9 in which said correction-inducing meansincludes a magnet bar secured to the horizontal gimbal ring of thegyroscope and a coil adjacent said ring, said coil being connectedacross said other diagonal of the bridge, whereby signals from thebridge create a unidirectional fiux in one or the other direction insaid bar to induce a corrective precessional action on said gyroscope torestore spatial alignment of the gyroscope and compass.

WILLIAM P. LEAR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,300,404 Carter et al Nov. 3,1942 2,356,186 Somers Aug. 22, 1944 2,403,091 Lear July 2, 1946 FOREIGNPATENTS Number Country Date 835,470 France Sept. 19, 1938

